Since the 19th century, there has been an increase in leisure time with much of that time being spent outdoors. As such, many baby boomers and young adults have had moderate to extensive unprotected sun exposure. Generally, the results of cumulative sun exposure are not clinically apparent for many decades after exposure. The first clinical signs of sun damage often are actinic keratoses (AKs) and sometimes nonmelanoma skin cancers. The treatment of AKs and nonmelanoma skin cancers can cause substantial morbidity and scarring, as well as cost millions of dollars annually. Various topical compositions for AKs and nonmelanoma skin cancers are indicated by the FDA for treatment. Clinicians use, for example, 5-fluorouracil (5-FU) cream, a fluorinated pyrimidine antimetabolite, for the topical treatment of solar or actinic keratoses (AKs). 5-FU is a chemocytotoxic agent, which means that it induces cell death upon uptake by receptive cells, such as cells that are actinically damaged. Rather than delaying treatment until the onset of clinically apparent sun damage, there is a need to reduce morbidity and scarring by prophylactically treating sun damage. That is, there is a need to treat subclinical sun damage.